1. Field Of the Invention
The present invention relates to asphaltic compositions for the preparation of bituminous draining or porous mixes and the preparation thereof.
2. Background
Conventional bituminous mixes are generally applied on most roads. However, the stresses to which these roads are subjected increase from year to year. Increasingly high axle loads and tire rolling pressures and the incessant increase in traffic have an unavoidable effect on the lifetime of these roads. More and more use is made of polymer-modified bitumens and of the development of new bituminous mix structures in order to combat the detrimental effects exerted by these traffic stresses.
The main technical objectives aimed at in the use of modified bitumens are:
(a) a greater resistance to permanent deformation; PA1 (b) an improved low-temperature fatigue resistance; and PA1 (c) an increase in the adhesive and cohesive properties. PA1 (a) Increased safety for the users: (i) elimination of the film of water on the highway preserves the ;adhesion of the tires to the ground, and this ensures a good trajectory and efficient vehicle braking; (ii) the driver is no longer dazzled by the multiple reflections of the many sources of light; and (iii) water spraying is eliminated. PA1 (b) Reduction in noise: better environmental protection is obtained by virtue of an increase in the sound-absorption properties, in order to lower the perceived noise level. PA1 (c) Reduction in costs: increased service life of the profiling and foundation layers by virtue of optimum water removal by the surface draining layer. PA1 (a) an inorganic skeleton or aggregate comprising (by weight): from 79 to 88 parts of macadam of 6/17 particle size (between 6 and 17 mm), from 9 to 15 parts of sand of 0.08/2 particle size, from 3 to 8 parts of inert filling material of particle size smaller than 0.08, calculated to obtain a total of 100 parts; PA1 (b) from 3.5 to 7 parts by weight of bitumen which has a penetration of between 65 and 150 tenths of mm at 25.degree. C.; PA1 (c) a first modifier chosen from the group comprising styrene-butadiene or styrene-isoprene copolymers or a mixture of such copolymers or of recycled tires, in a quantity corresponding to 2 to 7% by weight, calculated on the mass of the bitumen, optionally extended with 0 to 3% by weight of oil, calculated on the mass of the bitumen; and PA1 (d) a second modifier chosen from the group comprising polyolefins, polyethylene terephthalate or a mixture of such polymers, in a quantity corresponding to 0.5 to 5 parts by weight:, without exceeding the quantity of bitumen. PA1 (a) an inorganic skeleton or aggregate comprising: PA1 (b) either PA1 (c) a second modifier chosen from the group comprising polyolefins, polyethylene terephthalate and mixtures of such polymers, in a quantity corresponding to 0.5 to 5 parts, calculated on the inorganic mass.
For many years attempts have been made in highway engineering to employ industrial byproducts and, among these, recovered plastics originating either directly from the industry or from household waste. Plastics are of particular interest both from the viewpoint of cost and from an ecological viewpoint. In fact, this application enables the plastic waste to be permanently removed and does not present the risks related to the possible presence of polluting agents in gas emissions during incineration.
In addition to elastomeric modifiers such as SBS (styrene-butadiene-styrene) block copolymers or SBR (styrene-butadiene rubber) type or EVA (ethylene-vinyl acetate) plastomers, recent attempts have been made to utilize waste from cable manufacture, consisting essentially of LDPE (low density polyethylene) mixed with PVC (polyvinyl chloride) and polystyrene, or mixtures of polymers in household goods. European patent application number EP-332245-A, filed by Enichem having (i) the title "Bituminous Composition for Road Surfacing, (ii) a filing date of Feb. 24, 1989 and (iii) a publication date of Sep. 13, 1989 relates to this general area.
Bituminous draining mixes or porous asphalts have been the object of much interest. They are currently the preferred surfacing compositions for freeways and roads carrying heavy traffic. Their advantages are well known and include the following:
The manufacture of bituminous draining mixes calls for much care. The components forming part of the composition must have specific properties. The properties are obtained by the creation of channels within the thickness of the asphalt, and therefore by increasing the void volume. As a result of the open structure of the surface layer, the binder is subjected to stresses which differ from those encountered with traditional bituminous surface layers. The traditional compositions cannot therefore be employed. In order to combat these effects efficiently and therefore to ensure the durability of the draining layers it is necessary to have a sufficiently thick film of binder around each chip as well as good binder/granulate adhesiveness. Mechanical cohesion of the bituminous mix is traditionally obtained by the addition of new (SBS) or recycled (ground tire) elastomers, the aim being to obtain a binder which is extremely viscous and elastic at the service temperatures. Bituminous compositions in which the polyolefin concentration is higher than 5% by weight of bitumen give binders which are unstable in storage, greatly hardened and exhibiting phenomena of shrinkage on cooling.